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15 Energy and Chemical Change BIGIDEA Write the Big Idea for this chapter. Chemical reactions usually absorb or release energy. Use the “What I Know” column to list the things you know about the Big Idea. Then list the questions you have about the Big Idea in the “What I Want to Find Out” column. As you read the chapter, fill in the “What I Learned” column. W What I Want to Find Out Copyright © McGraw-Hill Education K What I Know Science Notebook • Energy and Chemical Change 253 L What I Learned 15 Energy and Chemical Change 1 Energy 2(G), 11(A), 11(B), 11(D) MAINIDEA Write the Main Idea for this lesson. Energy can change form and flow, but it is always conserved. REVIEW VOCABULARY Recall the definition of the Review Vocabulary term. temperature temperature a measure of the average kinetic energy of the particles in a sample of matter NEW VOCABULARY Define each New Vocabulary term. energy energy the ability to do work or produce heat law of conservation of energy Chemical potential energy law of conservation of energy heat reaction or physical process, energy can be converted from one form to calorie another, but it is neither created nor destroyed joule Chemical potential energy law stating that in any chemical the energy stored in a substance because specific heat of its composition heat energy that is in the process of flowing from a warmer object to a calorie the amount of heat required to raise the temperature of one gram of pure water one degree Celsius (1ºC) joule SI unit for heat and energy; one joule is equivalent to 0.2390 calories specific heat the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius Science Notebook • Energy and Chemical Change 254 Copyright © McGraw-Hill Education cooler object 1 Energy (continued) Use with pages 516–518. Compare and contrast kinetic energy with potential energy. Kinetic energy is the energy of motion. Potential energy is energy of the composition or position of an object. On the curve below that represents the skier on a ski slope on page 516, label the place of greatest kinetic energy A, least kinetic energy B, greatest potential energy C, and least potential energy D. B C A D Describe the skier above as a function of the law of conservation of energy. Before the skier starts, there is potential energy that is converted to kinetic energy, then to potential energy as the skier stops. Energy changes form. Explain chemical potential energy. Chemical potential Copyright © McGraw-Hill Education arrangement of its energy of a substance is a result of the atoms and the strength of the chemical bonds joining the atoms. During some chemical reactions, such as burning fuel , much of the potential energy may be released as heat . Some of the energy may be converted to work, which is a form of kinetic GET IT? State the law of conservation of energy in your own words. energy. Energy may change forms but is never gained or lost. Science Notebook • Energy and Chemical Change 255 1 Energy (continued) Use with pages 519–521. Identify each symbol in the equation for specific heat. q = c × m × ΔT q represents heat absorbed or released c represents the specific heat of the substance m represents mass of a sample in grams ΔT represents a change in temperature Summarize. Fill in the blanks to help you take notes while you read Example Problem. Problem The temperature of a sample of iron with a mass of 10.0 g changed from 50.4°C to 25.0°C with the release of 114 J heat. Determine the specific heat of iron. 1. Analyze the Problem Known: Unknown: energy released = 114 J ΔT = specific heat of iron = ? 50.4°C – 25.0°C = 25.4°C mass of iron = 10.0 g 2. Solve for the Unknown Write the equation for heat absorption. q = c × m × ΔT c= c= q m × ΔT 114 J (10.0g) (25.4°C) =0.499 J / (g.°C) 3. Evaluate the Answer If the values used in the calculations have three significant figures, the answer must also have three significant figures. The calculated value matches the value for iron in Table 2. Science Notebook • Energy and Chemical Change 256 Copyright © McGraw-Hill Education Solve for c. q = c × m × ΔT m × ΔT 1 Energy (continued) REVIEW IT ! 7. MAINIDEA Explain how energy changes from one form to another in an exothermic reaction. In an endothermic reaction. Chemical potential energy changes to heat in exothermic reactions, and the heat is released. In endothermic reactions, heat is absorbed and changed to chemical potential energy. 8. Distinguish between kinetic and potential energy in the following examples: two separated magnets; an avalanche of snow; books on library shelves; a mountain stream; a stock-car race; separation of charge in a battery. Two separated magnets illustrate potential energy. In a snow avalanche, positional potential energy changes to kinetic energy. Books on a shelf illustrate positional potential energy. As water races down a mountain stream, positional potential energy changes to kinetic energy. In a stock car race, chemical potential energy changes to kinetic energy. The separation of charge in a battery illustrates electrical potential energy. 9. Explain how the light and heat of a burning candle are related to chemical potential energy. Chemical potential energy, contained in the candle, is changed to energy in the form of light and heat Copyright © McGraw-Hill Education and released as the chemical combustion reaction takes place. 10. Calculate the amount of heat absorbed when 5.50 g of aluminum is heated from 25.0°C to 95.0°C. The specific heat of aluminum is 0.897 J/(g∙°C). 345 J 11. Interpret Data Equal masses of aluminum, gold, iron, and silver were left to sit in the Sun at the same time and for the same length of time. Use Table 2 to arrange the four metals according to the increase in their temperatures from largest increase to smallest. The temperature change is inversely proportional to specific heat: aluminum, iron, silver, gold. Science Notebook • Energy and Chemical Change 257